Optical reagent format for small sample volumes

ABSTRACT

An optical waveguiding optical format enables consistent optical analysis of small sample volumes with minimal variation in light path length among optical formats. The optical format is comprised of an input guide, an output guide, and a sample cavity adapted to allow light to pass through a sample on its way from the input guide to the output guide. A lid removed from the light pathway within the format may be provided with a reagent for assisting fluid analysis.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of prior U.S. patent application Ser. No. 10/694,376, filed Oct. 27, 2003, which claims the benefit of prior U.S. Provisional Patent Application No. 60/421,641, filed Oct. 29, 2002, both of which are hereby incorporated by reference herein in their entireties.

FIELD OF THE INVENTION

The present invention relates generally to medical testing and more specifically to an improved format for optical testing of fluids.

BACKGROUND OF THE INVENTION

Optical testing of samples has become increasingly popular in recent years due to the speed, accuracy, and efficiency with which test results can be acquired through optical testing. Because of these benefits, optical testing is commonly used in medical applications such as glucose testing. Generally, optical testing in medical applications involves passing light through a sample. In some applications, the sample may be combined with a reagent for testing. Upon passing through the sample or the combined sample and reagent, the test light is altered based on the qualities of the sample or sample/reagent combination. The light which passes through the sample comprises a detection beam which is input into a detector for analysis. Optical testing may employ “formats,” objects upon which a sample may be collected and which allow for easy transport and testing of a sample.

Several problems arise in optical testing applications. One common problem is the contamination of equipment optics when a sample is input for analysis. Such contamination may require error detection for contaminated optics and/or major cleaning procedures for the user, and further results in overall contamination of an analysis instrument. Such contamination may result, for example, from a close proximity of a light source or light detector to the sample application area of a format. Further, in applications using optical formats (i.e., testing formats with optical components through which light travels), the variation of the length of the path through which light travels can lead to variable testing accuracy. Optical formats often incorporate lids that are within the light path, which can add to the variability of light path length. Additionally, when testing particularly small sample volumes, it is desirable to use a short path length and further to eliminate the need for any path length variation technique in the testing instrument. Other problems that arise in the use of formats for optical testing include the need for optimization of reagent deposition into the format and the need for a separate format and a device, such as a needle or lancet, for placing a sample into the format.

In order to increase the efficiency and accuracy of optical sample testing, it is desirable to reduce or eliminate these known problems.

SUMMARY OF THE INVENTION

According to one embodiment of the present invention, an optical format isolates source and detection optics from a sample application area using a molded plastic light pipe.

According to another embodiment of the present invention, an optical format is provided with a light pipe which guides input light through a sample and guides the resulting detection light back toward a detector.

According to another embodiment of the present invention, an optical format including a light pipe for guiding light through a sample is further provided with a lid at an angle to the sample such that the lid is not within the light path within the sample.

According to another embodiment of the present invention, a microfabricated optical format is provided with a short path length and allows for minimal path length variation between individual formats.

According to yet another embodiment of the present invention, a format design including several options for reagent deposition into the format is provided.

According to still another embodiment of the present invention, an optical format having a wave guide is provided with an integrated lancet needle.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top view of an optical format according to the present invention;

FIG. 2 is a front view of an optical format according to the present invention;

FIG. 3 is a side view of an optical format according to the present invention;

FIG. 4 is an isometric view of an optical format according to the present invention;

FIG. 5 is a top view of an alternative optical format according to the present invention;

FIG. 6 is a cross-sectional view of the section defined by the line 6-6 in FIG. 5;

FIG. 7 is a front view of an alternative optical format according to the present invention;

FIG. 8 is a perspective view of an alternative optical format according to the present invention;

FIG. 9 is a top view of another alternative optical format according to the present invention;

FIG. 10 is a side view of another alternative optical format according to the present invention;

FIG. 11 is a front view of another alternative optical format according to the present invention;

FIG. 12 is a cross-sectional view of the section defined by the line 12-12 in FIG. 11;

FIG. 13 is an isometric view of another alternative optical format according to the present invention;

FIG. 14 is a front view of a sample cavity according to one embodiment of the present invention;

FIG. 15 is a side view of a sample cavity according to one embodiment of the present invention; and

FIG. 16 is an isometric view of a sample cavity according to one embodiment of the present invention.

While the invention is susceptible to various modifications and alternative forms, specific embodiments are shown by way of example in the drawings and will be described in detail herein. However, it should be understood that the invention is not intended to be limited to the particular forms disclosed. Rather, the invention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims.

DESCRIPTION OF SPECIFIC EMBODIMENTS

FIG. 1 shows an optical format 10 according to the present invention. The optical format 10 may be used in the collection and optical testing of samples, for example in medical testing applications such as glucose testing. The optical format 10 may be created using a variety of fabrication techniques, described more fully below, and may be constructed of such materials as polycarbonate, polystyrene or other plastics having the proper optical transmission characteristics.

An optical format 10 according to the present invention is provided with an input light guide 12 and an output light guide 14. The light guides could alternatively be considered “waveguides” or “light pipes.” The input light guide 12 guides light from a light input 16 toward an input reflector 18. The input reflector 18 reflects the light through a sample cavity 20, where the light interacts with a sample or a combination of sample and reagent. For example, reagents that allow glucose measurements may be used. From the sample cavity 20, the light continues toward an output light reflector 22. The output reflector 22 reflects light through the output light guide 14, which guides the light to a light output 24 where it then enters the detection optics in the meter (not shown). According to one embodiment of the present invention, the optical format 10 is further provided with a venting channel 26, which works either with or without a lancet to allow venting or vacuuming of the sample cavity 20. According to one embodiment of the present invention 10, the input reflector 18 and output reflector 22 utilize total internal reflection to guide light respectively toward and away from the sample cavity 20. The surfaces of one or both of the input reflector 18 and output reflector 22 may be provided with reflective coatings.

The optical format 10 is designed to be mounted in an analyzing instrument (not shown) and aligned with source and detection optics. In the embodiment shown in FIG. 1, the input reflector 18 is disposed at a 45-degree angle to the input light guide 12 and the output reflector 22 is disposed at a 45-degree angle to the output light guide 14, though greater or lesser angles are contemplated depending on the specific application for the format 10. The optical format 10 allows for the isolation of light source optics and light detection optics (not shown) from the sample cavity 20. According to one embodiment of the optical format 10, the input light guide 12 and output light guide 14 are of sufficient length to allow a sample to be kept outside of an instrument for optical measurement of the sample.

Turning now to FIG. 2, a front view of the optical format 10 is shown, more clearly illustrating the structure of one embodiment of the sample cavity 20. The sample cavity 20 is shown in contact with the venting channel 26. Also visible in FIG. 2 is a full lid 28, which covers one surface of the optical format 10. The full lid 28 is beneficial in applications utilizing a reagent deposited on the lid 28 prior to lamination of the lid to a surface of the optical format 10. Further, it is to be noted that the lid 28 is parallel to the direction of light travel through the sample cavity 20 and does not constitute a portion of the light travel path. Depending on the application, it may be beneficial to provide a lid disposed at alternative angles to the direction of light travel, or covering the sample cavity 20 from different directions.

As can be seen more clearly in FIG. 3, the sample cavity 20 extends inwardly from a sample-side surface 30 of the optical format 10. FIG. 4 shows an isometric view of the optical format 10, further illustrating the relationships of its individual portions.

In use, the sample cavity 20 serves as a capillary gap for a cuvette-type cell holding a sample. During sample collection, sample-side surface 30 of the optical format 10 may be placed against the skin, with a lancet 19 placed through the venting channel 26. The lancet 19 may be moved relative to the format 10 in the directions shown by arrow “A” of FIG. 4. The lancet is provided to pierce the skin and further to apply a vacuum to the flesh after lancing. It is to be understood that each embodiment of a format according to the present invention may be provided with or without a lancet depending on particular format applications. The fluid sample is thus drawn or wicked into the sample cavity 20 where it may interact with a reagent provided on the lid 28. Once the sample has been acquired, a light source (not shown) directs light into the light input 16, and a transmission reading is taken at a given wavelength or wavelengths after the light has passed through the sample. These results may be analyzed or converted to a reading corresponding to the amount or concentration of glucose or other analyte of interest, and this reading may be displayed to the user. Following use of an optical format according to the present invention, the optical format may be discarded.

The present invention allows for several methods of application of a reagent into an optical format. In addition to providing a reagent on the lid 28 before construction of an optical format, other methods of providing a reagent may be used. For example, reagent may be deposited into the sample cavity 20 before the optical format 10 is fully assembled or it may be wicked into the optical format 10 after the format is assembled and dried.

Turning now to FIGS. 5-8, an alternative embodiment of an optical format 32 according to the present invention is shown. FIG. 5 is a top view of the optical format 10, and FIG. 6 is a cross-sectional view along the line “6-6” of FIG. 5. FIG. 7 is a front view of the optical format 10 and FIG. 8 is an isometric view of the optical format 10. The primary difference between the optical format 10 of FIGS. 5-8 is the use of a shorter lid 34 and a light transmission segment 36 which extends beyond the dimensions of the input light guide 12 and output light guide 14. This design allows the conservation of materials in the light guide portions as compared to the light transmission segment 36, which may be provided with greater dimensions to accommodate a lancet (not shown), the lid 34, and a reagent (not shown) and further to allow room for sample to be input into the sample cavity 20. In addition, this design reduces the amount of light that is lost when the light passes through the non-sample portion of the transmission segment 36. The lid 34 may be printed with a reagent, or a reagent may be provided on the lid via alternative methods such as screen printing, microdeposition, pin deposition, or as a matrix label containing the reagent.

Turning now to FIG. 9, an alternative embodiment of an optical format 38 is shown. The optical format 38 of this embodiment is provided without a lid. FIG. 9 shows a top view of an optical format 38 having a sample cavity 40 provided therein. FIG. 10 shows a side view of the optical format 38 and illustrates that the sample cavity 40 is bounded along one side by a cavity base 42. According to one embodiment, the cavity base 42 is integral with the remainder of the optical format 38.

Turning now to FIG. 11, a front view of the optical format 38 is shown, further illustrating the relationship between the sample cavity 40 and the cavity base 42. FIG. 12 shows a cutaway view along the line “12-12” of FIG. 11 and further shows the dimensions of one embodiment of a sample cavity 40 according to the present invention. According to this embodiment, the cavity base 42 has a length, l_(CB), of about 0.70 inches, and the sample cavity 40 has a height, h_(SC), of about 0.035 inches, though it is contemplated that greater or lesser dimensions could be formed based on particular applications.

FIG. 13 is an isometric view of the optical format 38, more clearly showing the location of the sample cavity 40 in relation to the other portions of the optical format. FIG. 14 is a front view of the sample cavity 40, showing the width, w_(MC), of a main cavity portion 44 and further showing the width, w_(VC), of a venting cavity 46. According to one embodiment of the optical format 38, the width, w_(MC), of the main cavity portion 44 is approximately 0.005 inches and the width, w_(VC), of the venting cavity 46 is approximately 0.002 inches, though it is to be understood that wider or narrower spacing may be used based on specific applications of the optical format 38. FIGS. 15 and 16, respectively, are a side view and an isometric view of the sample cavity. According to one embodiment, the sample cavity 40 has a depth, d_(sc), of about 0.035 inches.

An optical format according to the present invention may be fabricated using a variety of techniques, including microfabrication techniques, which can replicate multiple tool cavities without any significant variations from product to product. One example of a microfabrication technique which may be used to create an optical format according to the present invention is the LIGA process. The LIGA process is named after a German acronym and uses X-ray deep-etch lithography and electroplating and molding to create small formations having significant differences between height and depth measurements, or high “aspect ratios.” Utilizing a microfabrication process, path length variation tolerance—that is, the difference in the distance of light travel in different optical formats—can be kept within an acceptable range, even when manufacturing extremely small optical formats. Depending upon the complexity of the format, the range may be within a few microns. Other microfabrication techniques which can be used to manufacture optical formats according to this invention include embossing of plastic sheets or the use of UV cure epoxy over master forms. Further, the capillary gap can be laser cut or molded via conventional molding.

Using an optical format according to the present invention, it is possible to perform accurate optical sample analysis on sample volumes in the range of from about 200 nl to about 500 nl, though optical formats may be adapted for use with larger or smaller volumes.

While the present invention has been described with reference to one or more particular embodiments, those skilled in the art will recognize that many changes may be made thereto without departing from the spirit and scope of the present invention. For example, while the present invention has been generally described as directed to medical applications it is to be understood that any optical fluid testing applications might employ the principles of the invention. Each of these embodiments and obvious variations thereof is contemplated as falling within the spirit and scope of the claimed invention, which is set forth in the following claims. 

1. A method of optically analyzing a fluid sample comprising: placing a sample-side surface of an optical format against a skin surface, the optical format including an optical communication path formed by an input light guide coupled with an input reflector, an output light guide coupled with an output reflector, and a sample cavity disposed between the input reflector and the output reflector, the optical communication path being continuous and closed between a first end of the input light guide and the input reflector and being continuous and closed between a first end of the output light guide and the output reflector; puncturing the skin surface with a lancet in communication with the sample cavity to obtain the fluid sample; collecting the fluid sample in the sample cavity; interacting the fluid sample with a reagent; directing light entering the input light guide through the sample cavity; detecting light which has passed through the sample cavity; and optically analyzing the fluid sample using the detected light.
 2. The method of claim 1, wherein the optical format further includes a venting channel connected to the sample cavity, and wherein the lancet is positioned within the venting channel.
 3. The method of claim 1, wherein the input light guide defines a first portion of the optical communication path, and wherein the input reflector is disposed at about a 45-degree angle to the first portion of the optical communication path.
 4. The method of claim 3, wherein the output light guide defines a second portion of the optical communication path, and wherein the output reflector is disposed at about a 45-degree angle to the second portion of the optical communication path.
 5. The method of claim 1, wherein the lancet has a first end for collecting test material and a second end for depositing test material within the sample cavity.
 6. The method of claim 1, wherein the input light guide is formed by a first four-sided wall structure and the output light guide is formed by a second four-sided wall structure.
 7. The method of claim 1, wherein the reagent is provided on a lid adjacent the sample cavity.
 8. A method of using an optical format, the method comprising: engaging the optical format against skin of a user, the optical format including an optical communication path formed by an input light guide coupled with an input reflector, an output light guide coupled with an output reflector, and a sample cavity disposed between the input reflector and the output reflector, the optical communication path being continuous and closed between the input light guide and the input reflector and being continuous and closed between the output light guide and the output reflector; receiving the fluid sample from the skin in the sample cavity; and directing light entering the input light guide through the sample cavity.
 9. The method of claim 8, further comprising puncturing the skin with a lancet in communication with the sample cavity and drawing the fluid sample from the user using the lancet.
 10. The method of claim 8, wherein the directing light entering the input light guide through the sample cavity includes directing light along the optical communication path from a light input, through the input light guide, to the input reflector, and then through the sample cavity.
 11. The method of claim 10, further comprising directing light which has passed through the sample cavity along the optical communication path from the sample cavity, to the output reflector, through the output light guide, and to a light output.
 12. The method of claim 11, further comprising detecting light which has passed through the sample cavity.
 13. The method of claim 12, further comprising determining an analyte concentration in the fluid sample using the detected light.
 14. A method for determining an analyte concentration in a fluid sample comprising: puncturing skin of a user with a lancet; allowing the fluid sample to accumulate on a surface of the skin; engaging an optical format against the skin of the user, the optical format including an optical communication path formed by an input light guide coupled with an input reflector, an output light guide coupled with an output reflector, and a sample cavity disposed between the input reflector and the output reflector, the input light guide being formed by a first four-sided wall structure and the output light guide being formed by a second four-sided wall structure, the optical communication path being continuous and closed between the input light guide and the input reflector and being continuous and closed between the output light guide and the output reflector; collecting at least a portion of the accumulated fluid sample in the sample cavity of the optical format; interacting the fluid sample with a reagent provided on a lid adjacent the sample cavity; directing light entering the input light guide through the sample cavity, at least a portion of the entering light passing through the sample cavity; detecting light which has passed through the sample cavity; and determining the analyte concentration in the fluid sample using the detected light.
 15. The method of claim 14, wherein the directing light entering the input light guide through the sample cavity includes directing light along the optical communication path from a light input, through the input light guide, to the input reflector, and then through the sample cavity.
 16. The method of claim 15, further comprising directing light which has passed through the sample cavity along the optical communication path from the sample cavity, to the output reflector, through the output light guide, and to a light output. 